Fuel cell cogeneration system

ABSTRACT

A fuel cell cogeneration system includes a fuel cell, a cooling water heat exchanger provided on a cooling water pathway, a stored hot water pathway through which stored hot water that exchanges heat with cooling water flows, a stored hot water tank, a stored hot water controlling device, a stored hot water temperature measuring device, a stored hot water flow rate adjusting device, a flow rate controlling device of controlling the stored hot water flow rate adjusting device and an exhaust gas heat exchanger of exchanging heat between exhaust gas from fuel processing devices and stored hot water. The flow rate controlling device controls the stored hot water adjusting device to reduce the flow rate of stored hot water flowing through the stored hot water pathway when the temperature of stored hot water is a first predetermined temperature or less during the starting of operation of the fuel cell.

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCTINTERNATIONAL APPLICATION PCT/JP2003/11997.

TECHNICAL FIELD

The present invention relates to a method of operating a fuel cellcogeneration system which performs electricity generation and heatsupply using a fuel cell and a program and recording medium therefor.

BACKGROUND ART

A fuel cell cogeneration system cannot generate electricity unless thetemperature of the fuel cell is raised to a predetermined temperatureand thus needs to be preheated during starting. In the related art fuelcell cogeneration system, a heater is used to heat cooling water bywhich the temperature of the fuel cell is then raised. However, thetemperature raising method using a heater has a disadvantage that theelectric power consumed during the starting of the fuel cellcogeneration system is great. Thus, a method has been proposed whichcomprises utilizing hot water stored in a stored hot water tank to raisethe temperature of the fuel cell during starting (see, e.g.,JP-A-2002-42841). The configuration of this method is shown in FIG. 4. Afuel cell 11 undergoes reaction of a hydrogen-rich gas (hereinafterreferred to as “fuel gas”) supplied and an oxidizer gas such as air togenerate electric power and heat. The fuel gas is produced by heating astarting material such as natural gas in an atmosphere containing watervapor in a fuel processing means 21. The oxidizer gas is supplied intothe fuel cell 11 by an air supplying unit 41.

Cooling water of supplying heat during starting to raise the temperatureof the fuel cell 11 and removing the heat generated during electricitygeneration to maintain the fuel cell 11 at a predetermined temperatureis circulated in the fuel cell 11 by a cooling water circulating pump12. The cooling water which has passed through the fuel cell 11 thenexchanges heat with stored hot water in a cooling water heat exchanger13. In a stored hot water tank 31 is stored hot water of recovering theheat generated by the fuel cell system.

During electricity generation, stored hot water is taken out of thestored hot water tank 31 at the bottom thereof by a waste heattransporting means 39 through which it is sent to a stored hot waterpathway 15, and then passed through the cooling water heat exchanger 13where it then exchanges heat with cooling water flowing through acooling water pathway 16. The stored hot water which has thus recoveredheat is then returned to the top of the stored hot water tank 31 by thewaste heat transporting means 39.

During starting, the pathway from the stored hot water 31 to the storedhot water pathway 15 is switched by the waste heat transporting means39. In other words, stored hot water is taken out of the top of thestored hot water tank 31, and then passed through the cooling water heatexchanger 13 where it supplies heat to cooling water, and the stored hotwater which has thus supplied heat to cooling water is then returned tothe bottom of the stored hot water tank 31. By thus transferring theheat of the stored hot water tank 31 to cooling water, the temperatureof the fuel cell 11 is raised. By raising the temperature of the fuelcell 11 with hot water in the stored hot water tank 31 in the aforesaidfuel cell cogeneration system, the electric power consumed duringstarting can be reduced.

Further, as another example, it has been proposed that an exhaust gasheat exchanger 23 of recovering heat from the fuel processing means 21is provided upstream the cooling water heat exchanger 13 on the storedhot water pathway 15, so that the heat recovered from exhaust gas istransferred to cooling water via the cooling water heat exchanger 13 toaccelerate the rise of temperature of the fuel cell as in a fuel cellcogeneration system shown in FIG. 5 (see, e.g., JP-A-2002-25591).

However, the fuel cell cogeneration system shown in FIG. 4 isdisadvantageous in that it takes much time to raise the temperature ofcooling water when the difference in temperature between the stored hotwater and the cooling water which exchange heat with each other issmall.

Further, even when only the heat recovered from exhaust gas is utilizedto raise the temperature of the fuel cell as in the fuel cellcogeneration system shown in FIG. 5, the time required to start the fuelcell cannot be sufficiently reduced. Thus, a configuration comprisingone shown in FIG. 4 and one shown in FIG. 5 in combination can beproposed, but even this case is disadvantageous in that the temperatureof the fuel cell cannot reach a desired operating temperature or, evenif the operating temperature is reached, the time required to start thefuel cell cannot be sufficiently reduced.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a fuel cellcogeneration system, a method of operating a fuel cell cogenerationsystem and a program and recording medium therefor which can raise thetemperature of the fuel cell in a short period of time to reduce thetime required until starting even when the difference in temperaturebetween stored hot water and cooling water is small in the light of theafore said problems.

To solve the above problems, a first aspect of the present invention isa fuel cell cogeneration system comprising:

-   -   a fuel cell connected to a fuel processing means and having a        cooling water pathway;    -   a first heat exchanging means provided on the aforesaid cooling        water pathway;    -   a stored hot water pathway through which stored hot water        undergoes heat exchange with the aforesaid cooling water via the        aforesaid first heat exchanging means;    -   a stored hot water tank of storing the aforesaid stored hot        water;    -   a stored hot water controlling means of circulating the        aforesaid stored hot water so as to transfer the heat of hot        water stored in the aforesaid stored hot water tank to the        aforesaid fuel cell via the aforesaid stored water pathway and        the aforesaid first heat exchanging means during the starting of        operation of the aforesaid fuel cell;    -   a stored hot water temperature measuring means of measuring the        temperature of stored hot water flown into the aforesaid first        heat exchanging means;    -   a stored hot water flow rate adjusting means of adjusting the        flow rate of stored hot water flowing through the aforesaid        stored hot water pathway;    -   a flow rate controlling means of controlling the aforesaid        stored hot water flow rate adjusting means on the basis of the        temperature of stored hot water measured by the aforesaid stored        hot water measuring means; and    -   a second heat exchanging means connected to the aforesaid stored        hot water pathway upstream the aforesaid first heat exchanging        means of exchanging heat with exhaust gas of the aforesaid fuel        processing means,    -   wherein the aforesaid flow rate controlling means controls the        aforesaid stored hot water flow rate adjusting means to reduce        the flow rate of stored hot water flowing through the aforesaid        stored hot water pathway when the temperature of the aforesaid        stored hot water is a first predetermined temperature or less        during the starting of operation of the aforesaid fuel cell.

A second aspect of the present invention is the fuel cell cogenerationsystem according to the first aspect of the present invention, whereinthe aforesaid first predetermined temperature is an operatingtemperature of the aforesaid fuel cell.

A third aspect of the present invention is the fuel cell cogenerationsystem of the first aspect of the present invention, wherein a coolingwater temperature measuring means is further provided upstream theaforesaid first heat exchanging means on the aforesaid cooling waterpathway and the aforesaid flow rate controlling means adjusts theaforesaid stored hot water flow rate adjusting means so that theaforesaid temperature of stored hot water rises to further reduce theflow rate of stored hot water flowing through the aforesaid stored hotwater pathway when the aforesaid temperature of stored hot water is lessthan the sum of the aforesaid cooling water temperature and apredetermined temperature.

A fourth aspect of the present invention is the fuel cell cogenerationsystem of the third aspect of the present invention, wherein theaforesaid flow rate controlling means adjusts the aforesaid stored hotwater flow rate adjusting means so that the aforesaid temperature ofstored hot water rises to a second predetermined temperature as upperlimit to reduce the flow rate of stored hot water flowing through theaforesaid stored hot water pathway and

-   -   the aforesaid second predetermined temperature is determined by        the temperature required to recover a predetermined amount of        water content contained in exhaust gas discharged by the        aforesaid fuel processing means in the aforesaid second heat        exchanging means.

A fifth aspect of the present invention is the fuel cell cogenerationsystem of the fourth aspect of the present invention, wherein arecovered water tank of recovering water content contained in exhaustgas discharged by the aforesaid fuel processing means and

-   -   the aforesaid second predetermined temperature is the        temperature at which a predetermined water level can be        maintained in the aforesaid recovered water tank while supplying        the aforesaid recovered water into the system.

A sixth aspect of the present invention is the fuel cell cogenerationsystem of the first or third aspect of the present invention, wherein arecovered water tank of recovering water content contained in exhaustgas discharged by the aforesaid fuel processing means is furtherprovided and

-   -   the aforesaid flow rate controlling means adjusts the aforesaid        stored hot water flow rate adjusting means to suspend the drop        of the flow rate of stored hot water flowing through the        aforesaid stored hot water pathway or to increase the flow rate        of the aforesaid stored hot water when the water level in the        aforesaid recovered water tank falls below the predetermined        value while supplying the aforesaid recovered water into the        system.

A seventh aspect of the present invention is the fuel cell cogenerationsystem of the first aspect of the present invention, wherein theaforesaid first predetermined temperature is predetermined within arange of from60° C. to 80° C.

An eighth aspect of the present invention is the fuel cell cogenerationsystem of the fourth aspect of the present invention, wherein theaforesaid second predetermined temperature is predetermined within arange of from 40° C. to 50° C.

A ninth aspect of the present invention is the fuel cell cogenerationsystem of the third aspect of the present invention, wherein theaforesaid predetermined temperature is predetermined within a range offrom 5° C. to 10° C.

A tenth aspect of the present invention is a method of operating a fuelcell cogeneration system comprising a step of circulating the aforesaidstored hot water so as to transfer the heat of hot water stored in theaforesaid stored hot water tank to the cooling water pathway of theaforesaid fuel cell via the aforesaid stored water pathway and theaforesaid first heat exchanging means during the starting of operationof the aforesaid fuel cell;

-   -   a step of measuring the temperature of stored hot water flown        into the aforesaid first heat exchanging means;    -   a step of transferring the heat of exhaust gas from the fuel        processing means to the aforesaid stored hot water via a second        heat exchanging means connected to the aforesaid stored hot        water pathway upstream the aforesaid first heat exchanging        means; and    -   a step of reducing the flow rate of stored hot water flowing        through the aforesaid stored hot water pathway when the        temperature of the aforesaid stored hot water is a first        predetermined temperature or less during the starting of        operation of the aforesaid fuel cell.

An eleventh aspect of the present invention is a program for the fuelcell cogeneration system of the first aspect of the present invention ofoperating a computer as a flow rate controlling means of controlling theaforesaid stored hot water flow rate adjusting means to reduce the flowrate of stored hot water flowing through the stored hot water pathwaywhen the temperature of the aforesaid stored hot water measured by theaforementioned stored hot water temperature measuring means is a firstpredetermined temperature or less during the starting of operation ofthe aforesaid fuel cell.

A twelfth aspect of the present invention is a recording medium having aprogram of the eleventh aspect of the present invention supportedthereon which can be processed by a computer.

In accordance with the present invention, a fuel cell cogenerationsystem, a method of operating a fuel cell cogeneration system and aprogram and recording medium therefor which can raise the temperature ofthe fuel cell in a short period of time to reduce the time requireduntil starting even when the difference in temperature between storedhot water and cooling water is small can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configurational diagram of a fuel cell cogeneration systemof embodiment 1 of implementation of the present invention.

FIG. 2 is a configurational diagram of a fuel cell cogeneration systemof embodiment 2 of implementation of the present invention.

FIG. 3 is a configurational diagram of a fuel cell cogeneration systemof embodiment 3 of implementation of the present invention.

FIG. 4 is a configurational diagram of a related art fuel cellcogeneration system.

FIG. 5 is a configurational diagram of another related art fuel cellcogeneration system.

DESCRIPTION OF SIGNS

-   -   11 Fuel cell    -   12 Cooling water circulating pump    -   13 Cooling water heat exchanger    -   14 Cooling water temperature measuring means    -   21 Fuel processing means    -   22 Combustor    -   23 Exhaust gas heat exchanger    -   31 Stored hot water tank    -   32 Stored hot water circulating pump    -   33 Stored hot water pathway switching means    -   34,35 Three-way valve    -   36 Stored hot water temperature measuring means    -   37 Flow rate controlling means    -   38 Flow rate adjusting means    -   39 Waste heat transporting means    -   41 Air supplying unit

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of implementation of the present invention will be describedhereinafter in connection with FIGS. 1 to 3.

Embodiment 1 of Implementation

The configuration of a fuel cell cogeneration system of an embodiment 1of implementation of the present invention is shown in FIG. 1. The fuelcell cogeneration system shown in FIG. 1 comprises a fuel cell 11 ofgenerating electric power and heat using a fuel gas and an oxidizer gassuch as air, a fuel processing means 21 of heating a starting materialto produce a fuel gas and supplying the fuel gas into the fuel cell 11,a combustor 22 disposed inside the fuel processing means 21 of heatingthe starting material, an air supplying means 41 of supplying anoxidizer gas into the fuel cell 11, a cooling water pathway 16 ofcirculating cooling water of keeping the fuel cell 11 at a predeterminedtemperature during the operation of the fuel cell cogeneration system, acooling water circulating pump 12 of circulating cooling water in thecooling water pathway 16, a cooling water heat exchanger 13 which isprovided on the cooling water pathway 16 as an example of the first heatexchanging means of the present invention to perform heat exchangebetween cooling water and stored hot water, a stored hot water tank 31of storing hot water, a stored hot water switching means 33 of switchingthe pathway from the stored hot water tank 31 to the stored hot waterpathway 15 using three-way valves 34 and 35 between during starting andduring electricity generation, a stored hot water circulating pump 32 ofcirculating stored hot water, and an exhaust gas heat exchanger 23 whichis connected to the point upstream the cooling water heat exchanger 13as an example of the second heat exchanging means of the presentinvention to recover heat and water from the exhaust gas from thecombustor 22. The fuel cell cogeneration system also comprises a storedhot water measuring means 36 of measuring the temperature of stored hotwater flown into the cooling water heat exchanger 13, a flow ratecontrolling means 37 of giving an instruction of controlling the flowrate of stored hot water in the stored hot water pathway 15 and a flowrate adjusting means 38 which is an example of stored hot water flowrate adjusting means of the present invention of adjusting the flow rateof stored hot water by an instruction from the flow rate controllingmeans 37, provided in the stored hot water pathway 15 between theexhaust gas heat exchanger 23 and the cooling water heat exchanger 13.

The arrows A and B in FIG. 1 indicate the flow of stored hot waterduring the electricity-generating operation of the fuel cellcogeneration system and the flow of stored hot water during starting,respectively.

Next, the operation of the fuel cell cogeneration system thus arrangedwill be described.

The operation during electricity-generating operation will be describedhereinafter.

The fuel processing means 21 heats a starting material such as naturalgas supplied externally in an atmosphere containing water vapor toproduce a fuel gas containing hydrogen. The fuel processing means 21 isheated by the combustor 22. The exhaust gas heat exchanger 23 transfersheat from the exhaust gas discharged from the combustor 22 to stored hotwater while recovering condensed water vapor from the exhaust gas.

The fuel cell 11 performs electricity generation from the fuel gas thusproduced and an oxidizer gas supplied from the air supplying unit 41.Cooling water is circulated via the fuel cell 11 by the cooling watercirculating pump 12 to remove the heat generated by electricitygeneration. The cooling water the temperature of which has been raisedis subjected to heat exchange with stored hot water in the cooling waterheat exchanger 13 to release heat. During the generation of electricity(during electricity-generating operation), the three-way valves 34, 35in the stored hot water pathway switching means 33 are switched to theside indicated by the arrow A, so that the stored hot water is taken outfrom the bottom of the stored hot water tank 31 and then circulated bythe stored hot water circulating pump 32 sequentially through variousheat exchangers, i.e., exhaust gas heat exchanger 23 and cooling waterheat exchanger 13 to recover heat. The stored hot water which has thusrecovered heat is then returned to the top of the stored hot water tank31. Thus, stored hot water the temperature of which has been raised issequentially supplied into the stored hot water tank 31 at the topthereof to perform lamination boiling.

Next, the operation of staring the fuel cell cogeneration system havingthe aforesaid arrangement will be described.

In order to start this fuel cell cogeneration system, it is necessarythat the temperature of the fuel cell 11 and the fuel processing means21 reach a predetermined reactivity temperature. To this end, it isnecessary that they be each preheated. The fuel processing means 21 isheated by the combustor 22 to raise its temperature. During starting,the three-way valves 34, 35 in the stored hot water pathway switchingmeans 33 are switched to the side indicated by the arrow B. In thismanner, the stored hot water pathway 15 is switched such that the heatof hot water stored in the stored hot water tank 31 is transferred tothe fuel cell 11. In other words, the heated water stored in the top ofthe stored hot water tank 31 is taken out and then circulated throughthe stored hot water pathway 15 by the stored hot water circulating pump32. The stored hot water flowing through the stored hot water pathway 15recovers heat from the exhaust gas in the exhaust gas heat exchanger 23to raise its temperature. The stored hot water the temperature of whichhas been thus raised undergoes heat exchange in the cooling water heatexchanger 13 with the cooling water which is being circulated throughthe cooling water pathway 16 to heat the cooling water. Thereafter, thestored hot water which has given heat to the cooling water is returnedto the bottom of the stored hot water tank 31. On the other hand, thecooling water thus heated flows through the fuel cell 11 to cause thefuel cell 11 to raise its temperature to a predetermined desiredtemperature required for electricity generation (operating temperatureof fuel cell as an example of the first predetermined temperature of thepresent invention).

The flow rate controlling means 37 adjusts the flow rate adjusting means38 to reduce the flow rate of stored hot water flowing through thestored hot water pathway 15 when the temperature of stored hot water atthe inlet of the cooling water heat exchanger 13 measured by the storedhot water temperature measuring means 36 is the desired temperature orless. As a result of the reduction of the flow rate of stored hot waterflowing through the stored hot water pathway 15, the temperature of thestored hot water rises, making the difference between the temperature ofstored hot water on the stored hot water pathway 15 side of the coolingwater heat exchanger 13 and the temperature of cooling water on thecooling water pathway 16 side of the cooling water heat exchanger 13greater and hence making it possible to efficiently transfer the heatstored in the stored hot water tank 31 and/or the heat generated in thefuel processing means 21 to the fuel cell 11. Accordingly, as a result,the time required until the temperature required to start the fuel cell11 is reached can be reduced.

Further, the drop of the flow rate of stored hot water is predeterminedsuch that the difference between the temperature of stored hot water andthe desired temperature can be kept at at least a predetermined valuewhen the temperature of stored hot water is raised.

And, when the temperature of the fuel cell 11 reaches the desiredtemperature to complete the preparation for electricity generation, thethree-way valves 34, 35 are switched to start normal operation.

Examples of such a desired temperature include 60° C. to 80° C. in thecase where the fuel cell 11 is of polymer electrolyte type. Preferredexamples of the difference between the temperature of stored hot waterand the desired temperature include 5° C. to 10° C.

In accordance with such a fuel cell cogeneration system, the heat storedin the stored hot water tank 31 during the operation of electricitygeneration can be utilized to raise the temperature of the fuel cell 11during starting. As a result, the electric power consumed duringstarting can be reduced, making it possible to enhance the efficiency ofthe fuel cell cogeneration system. Further, by recovering heat from theexhaust gas so that the stored hot water can further raise itstemperature and undergoes heat exchange with cooling water in thecooling water heat exchanger 13, the temperature difference betweenstored hot water and cooling water can be made greater, making itpossible to reduce the time required to raise the temperature of thefuel cell 11.

In addition, even when the temperature of hot water stored in the storedhot water 31 is less than the desired temperature for raising thetemperature of the fuel cell 11, the heat of the exhaust gas from thecombustor 22 can be recovered in the exhaust gas heat exchanger 23 toraise the temperature of the fuel cell 11 to the desired temperature.

Further, the flow rate of stored hot water can be adjusted so as to keepthe temperature of stored hot water in the cooling water heat exchanger13 constant or more, making it possible to reduce the time required toraise the temperature of the fuel cell 11. Moreover, when the differencein temperature between stored hot water and cooling water in the coolingwater heat exchanger 13 is kept constant or more, the time required toraise the temperature of the fuel cell 11 can be further reduced.

In accordance with the cogeneration system of the present embodiment,when the fuel cell system is used at home for example, the use of heatfrom the stored hot water tank 31 is little limited even during thestarting of the fuel cell, making it possible to sufficiently use heatat home.

Embodiment 2 of Implementation

FIG. 2 is a configurational diagram illustrating a fuel cellcogeneration system in the embodiment 2 of implementation of the presentinvention. The same constituent elements as in Embodiment 1 ofimplementation are given the same reference numerals and theirdescription will be omitted. The fuel cell cogeneration system of thepresent embodiment of implementation of the invention further comprisesas a constituent element a cooling water temperature measuring means 14provided upstream the cooling water heat exchanger 13 of measuring thetemperature of cooling water at the inlet of the cooling heat exchanger13. And, the flow rate controlling means 37 further has a function ofadjusting the flow rate of stored hot water flowing through the storedhot water pathway 15 on the basis of the temperature of stored hot waterand the temperature of cooling water by the flow rate adjusting means38.

The operation of the fuel cell cogeneration system of the presentembodiment thus arranged during starting will be described hereinafter.The description of the same operation as in Embodiment 1 ofimplementation will be omitted.

The hot water thus heated and stored in the stored hot water 31undergoes heat exchange with the cooling water in the cooling water heatexchanger 13 to heat the cooling water. At this time, the flow ratecontrolling means 37 controls the flow rate adjusting means 38 to adjustthe flow rate of stored hot water such that the difference between thetemperature of cooling water measured by the cooling water temperaturemeasuring means 14 and the temperature of stored hot water measured bythe stored hot water measuring means 36 is a predetermined value or moreand the temperature of stored hot water reaches minimum while satisfyingthe requirement. In other words, when the difference between thetemperature of cooling water and the temperature of stored hot water isless than the predetermined temperature difference (that is, when thetemperature of stored hot water is less than the sum of the temperatureof cooling water and a predetermined temperature), the flow ratecontrolling means 37 gives an instruction to the flow rate adjustingmeans 38 to reduce the flow rate of stored hot water flowing through thestored hot water pathway 15.

However, at this time, the flow rate controlling means 37 causes theflow rate adjusting means 38 to predetermine the flow rate of stored hotwater such that the temperature of stored hot water reaches a secondpredetermined temperature or less. The term “second predeterminedtemperature” as used herein means the upper limit of temperaturerequired to recover a predetermined amount of water content contained inthe exhaust gas discharged from the fuel processing means 21 in theexhaust gas heat exchanger 23. Examples of such an upper limit include40° C. to 50° C.

The stored hot water which has been subjected to heat exchange in theexhaust gas heat exchanger 23 and the cooling water heat exchanger 13 isthen returned to the bottom of the stored hot water tank 31.

In accordance with the constitution of the fuel cell cogeneration systemof the present embodiment, the flow rate of stored hot water can beadjusted to keep the difference between the temperature of stored hotwater in the cooling water heat exchanger 13 and the temperature ofcooling water in the cooling water heat exchanger 13 constant or moreand keep the temperature of the stored hot water outlet of the exhaustgas heat exchanger 23 (i.e., temperature of the stored hot water inletof the cooling water heat exchanger 13) at the second predeterminedtemperature or less. As a result, the time required to raise the fuelcell 11 can be reduced and the amount of water recovered in the exhaustgas heat exchanger 23 can be maintained at a predetermined value ormore.

While Embodiments 1 and 2 of implementation have been described withreference to the case where the flow rate of stored hot water isadjusted by the flow rate adjusting means 38, the stored hot water flowrate adjusting means of the present invention may be integrated with thestored hot water circulating pump 32 such that the flow rate of storedhot water is adjusted by the amount operated by the stored hot waterpump 32. In this case, the arrangement may be made such that when theflow rate controlling means 37 gives an instruction of reducing the flowrate of stored hot water, the amount operated by the stored hot waterpump 32 is adjusted according to the instruction, and, in this case,too, the same effect as mentioned above can be exerted.

Embodiment 3 of Implementation

The fuel cell cogeneration system of the present embodiment ofimplementation of the invention shown in FIG. 3 comprises a recoveredwater tank 51 connected to the exhaust gas heat exchanger 23. Inside therecovered water tank 51 is provided a water amount measuring means 52 ofdetecting the amount of water (water level) recovered from the exhaustgas heat exchanger 23. The water amount measuring means 52 is connectedto the flow rate controlling means 37.

Next, the operation of the fuel cell cogeneration system of the presentembodiment will be described.

The hot water thus heated and stored in the stored hot water tank 31undergoes heat exchange with the cooling water in the cooling water heatexchanger 13 to heat the cooling water. At this time, the flow ratecontrolling means 37 controls the flow rate adjusting means 38 to adjustthe flow rate of stored hot water such that the difference between thetemperature of cooling water measured by the cooling water temperaturemeasuring means 14 and the temperature of stored hot water measured bythe stored hot water measuring means 36 is a predetermined value or moreand a water level in the recovered water tank 51 is kept whilesatisfying the requirement. In other words, when the difference betweenthe temperature of cooling water and the temperature of stored hot wateris the predetermined temperature difference or less, the flow ratecontrolling means 37 gives an instruction to the flow rate adjustingmeans 38 to reduce the flow rate of stored hot water flowing through thestored hot water pathway 15.

The water which has been recovered by the recovered water tank 51 isthen supplied into various portions of the fuel cell cogenerationsystem. Accordingly, when the amount of water recovered from the exhaustgas heat exchanger 23 (amount of water entering into the recovered watertank 51 in a predetermined period of time) and the flow rate of watersupplied into the various portions from the recovered water tank 51(amount of water discharged from the recovered water tank 51 in theaforesaid predetermined period of time) are balanced, the water level inthe recovered water tank 51 is kept constant. When the flow rate ofwater recovered from the exhaust gas heat exchanger 23 is small ascompared with the flow rate of water supplied from the recovered watertank 51, the water level in the recovered water tank 51 lowers.

When the water amount measuring means 52 detects that the water level inthe recovered water tank 51 reaches a predetermined level or less, theflow rate controlling means 37 adjusts the flow rate adjusting means 38to adjust the drop of the flow rate of stored hot water flowing throughthe stored hot water pathway 15 such that the amount of water recoveredby the recovered water tank 51 increases until the water level in therecovered water tank 51 reaches the predetermined water level. When thewater level in the tank 51 doesn't reach the predetermined value, theflow rate controlling means 37 adjusts the flow rate adjusting means 38to increase the flow rate of stored hot water flowing through the storedhot water pathway 15 under the condition that the difference between thetemperature of cooling water and the temperature of stored hot water isthe predetermined value or more. When the flow rate of stored hot waterincreases, the temperature of stored hot water falls, causing the amountof condensed water vapor recovered in the exhaust gas heat exchanger 23to rise. In other words, the flow rate of stored hot water is reducedsuch that the difference between the temperature of cooling water andtemperature of stored hot water reaches the predetermined value or moreunder the condition that the water level in the recovered water tank 51is maintained at the predetermined value. As a result, the flow rate ofwater entering the recovered water tank 51 is greater than the flow rateof water discharged from the recovered water tank 51, causing the waterlevel in the recovered water tank 51 to rise.

Thus, in accordance with the fuel cell cogeneration system of thepresent embodiment, the amount of water recovered in the exhaust gasheat exchanger 23 can be kept at a value required to operate the systemwhile reducing the time required to raise the temperature of the fuelcell during starting.

Embodiment 2 of implementation has been described with reference to thecase where the amount of water recovered in the exhaust gas heatexchanger 23 is maintained such that the temperature of stored hot waterreaches the second predetermined temperature or less, but the secondpredetermined temperature corresponds to the temperature of stored hotwater developed when the predetermined water level in the recoveredwater tank 51 is maintained as described in the present embodiment.

As mentioned above, in accordance with the constitution of the fuel cellcogeneration system of the present invention, the heat of hot waterstored in the stored hot water tank during the starting of electricitygeneration operation can be utilized to reduce the time required toraise the temperature of the fuel cell.

While the description has been made with reference to the case where thestored hot water tank of the present invention is of lamination boilingtype, other types of stored hot water tank may be used, and, in thiscase, too, the same effect as mentioned above can be exerted.

Further, while the description has been made with reference to the casewhere all the heat generated by the fuel cell 11 is stored in the storedhot water tank 31 during the operation of the fuel cell cogenerationsystem of the present invention, part of the heat generated by the fuelcell 11 may be stored in the stored hot water tank 31, and, the sameeffect as mentioned above can be exerted if stored hot water thetemperature of which is higher than ordinary temperature is suppliedfrom the stored hot water tank 31 during the starting of the fuel cellcogeneration system of the present invention. Further, even when thetemperature of hot water stored in the stored hot water tank 31 is nothigher than ordinary temperature, heat exchange can be effected in theexhaust gas heat exchanger 23, and, in this case, too, the same effectas mentioned above can be exerted.

Moreover, while the description has been made with reference to the casewhere the stored hot water controlling means of the present invention isformed by the three-way valves 34, 35, the stored hot water controllingmeans may be arranged such that the pathway from the stored hot watertank 31 to the stored hot water pathway 15 is switched by other means,and, in this case, too, the same effect as mentioned above can beexerted.

Further, while the description has been made with reference to the casewhere the second heat exchanging means of the present inventioncomprises the exhaust gas heat exchanger 23 formed separately of fuelprocessing means, the second heat exchanging means of the presentinvention may be formed integrally with the fuel processing means of thepresent invention, and, the same effect as mentioned above can beexerted so far as it is arranged such that the exhaust gas dischargedfrom the fuel processing means of the present invention undergoes heatexchange with stored hot water.

Moreover, while the description has been made with reference to the casewhere the first predetermined temperature of the present invention isthe operating temperature of the fuel cell, the first predeterminedtemperature of the present invention may be higher than the operatingtemperature of the fuel cell. Further, in the case where the temperatureof stored hot water is controlled to the second predeterminedtemperature or less, the first predetermined temperature of the presentinvention may be temporarily lower than the operating temperature.

The present invention also concerns a program of executing the functionof all or part of units or devices of the flow rate controlling means ofthe aforementioned fuel cell cogeneration system of the presentinvention by computer, including a program operating in cooperation withcomputer.

The present invention further concerns a medium having a program ofexecuting the function of all or part of units or devices of the flowrate controlling means of the aforementioned fuel cell cogenerationsystem of the present invention by computer supported thereon, includinga computer-readable medium from which the aforementioned program can beread to execute the aforementioned function in cooperation with theaforementioned computer.

Further, the term “part of units or devices” as used herein means someof the plurality of units or devices or part of functions or operationsof one unit or device.

Moreover, the term “part of units or devices” as used herein means someof the plurality of units or devices or some of units or devices of oneunit or device or some functions of one unit.

Further, a computer-readable recording medium having a program of thepresent invention recorded thereon is included in the present invention.

Moreover, one of the working forms of the program of the presentinvention may be such that the program is recorded in acomputer-readable recording medium to operate in cooperation withcomputer.

Further, another working form of the program of the present invention issuch that the program is transmitted by the transmission medium and thenread by computer to operate in cooperation with computer.

Examples of the recording medium include ROM, etc. and examples of thetransmission medium include transmission media such as internet, light,electrical radiation, sound wave, etc.

Further, the aforesaid computer of the present invention is not limitedto sheer hardwares such as CPU but may include farmware, OS, andperiphery.

As mentioned above, the constitution of the present invention may berealized on a software basis or hardware basis.

In accordance with the fuel cell cogeneration system, method ofoperating the fuel cell cogeneration system and program and recordingmedium therefor according to the present invention, the temperature ofcooling water can be raised in a short period of time even when thedifference between the temperature of stored hot water and thetemperature of cooling water is small, making it possible to reduce thetime required for starting, and they are useful for the fuel cellcogeneration system having a stored hot water tank, etc.

1. A fuel cell cogeneration system comprising: a fuel cell connected toa fuel processing means and having a cooling water pathway, throughwhich cooling water flows; a first heat exchanging means provided on thecooling water pathway; a stored hot water pathway through which storedhot water undergoes heat exchange with the cooling water via the firstheat exchanging means; a hot water tank for storing the hot water; astored hot water controlling means of circulating the stored hot waterso as to transfer the heat of hot water stored in the stored hot watertank to the fuel cell via the stored water pathway and the first heatexchanging means during the starting of operation of the fuel cell; astored hot water temperature measuring means of measuring thetemperature of stored hot water flowing into the first heat exchangingmeans; a stored hot water flow rate adjusting means of adjusting theflow rate of stored hot water flowing through the stored hot waterpathway; a flow rate controlling means of controlling the stored hotwater flow rate adjusting means on the basis of the temperature ofstored hot water measured by the stored hot water measuring means; and asecond heat exchanging means connected to the stored hot water pathwayupstream of the first heat exchanging means of exchanging heat withexhaust gas of the fuel processing means, wherein the flow ratecontrolling means controls the stored hot water flow rate adjustingmeans to reduce the flow rate of stored hot water flowing through thestored hot water pathway when the temperature of the stored hot water isa first predetermined temperature or less during the starting ofoperation of the fuel cell.
 2. The fuel cell cogeneration systemaccording to claim 1, wherein the first predetermined temperature is anoperating temperature of the fuel cell.
 3. The fuel cell cogenerationsystem according to claim 1, wherein a cooling water temperaturemeasuring means is further provided upstream of the first heatexchanging means on the cooling water pathway and the flow ratecontrolling means adjusts the stored hot water flow rate adjusting meansso that the temperature of stored hot water rises to further reduce theflow rate of stored hot water flowing through the stored hot waterpathway when the temperature of stored hot water is less than the sum ofthe cooling water temperature and a predetermined temperature.
 4. Thefuel cell cogeneration according to claim 3, wherein the flow ratecontrolling means adjusts the stored hot water flow rate adjusting meansso that the temperature of stored hot water rises to a secondpredetermined temperature as upper limit to reduce the flow rate ofstored hot water flowing through the stored hot water pathway and thesecond predetermined temperature is determined by the temperaturerequired to recover a predetermined amount of water content contained inexhaust gas discharged by the fuel processing means in the second heatexchanging means.
 5. The fuel cell cogeneration system according toclaim 4, wherein a recovered water tank of recovering water contentcontained in exhaust gas discharged by the fuel processing means and thesecond predetermined temperature is the temperature at which apredetermined water level can be maintained in the recovered water tankwhile supplying the recovered water into the system.
 6. The fuel cellcogeneration system according to claim 1 or 3, wherein a recovered watertank of recovering water content contained in exhaust gas discharged bythe fuel processing means is further provided and the flow ratecontrolling means adjusts the stored hot water flow rate adjusting meansto suspend the drop of the flow rate of stored hot water flowing throughthe stored hot water pathway or to increase the flow rate of the storedhot water when the water level in the recovered water tank falls belowthe predetermined value while supplying the recovered water into thesystem.
 7. The fuel cell cogeneration system according to claim 1,wherein the first predetermined temperature is predetermined within arange of from 60° C. to 80° C.
 8. The fuel cell cogeneration systemaccording to claim 4, wherein the second predetermined temperature ispredetermined within a range of from 40° C. to 50° C.
 9. The fuel cellcogeneration system according to claim 3, wherein the predeterminedtemperature is predetermined within a range of from 5° C. to 10° C. 10.A method of operating a fuel cell cogeneration system comprising: a stepof circulating stored hot water so as to transfer the heat of hot waterstored in a stored hot water tank to a cooling water pathway of a fuelcell via a stored water pathway and a first heat exchanging means duringthe starting of operation of the fuel cell; a step of measuring thetemperature of stored hot water flowing into the first heat exchangingmeans; a step of transferring the heat of exhaust gas from a fuelprocessing means to the stored hot water via a second heat exchangingmeans connected to the stored hot water pathway upstream of the firstheat exchanging means; and a step of reducing the flow rate of storedhot water flowing through the stored hot water pathway when thetemperature of the stored hot water is a first predetermined temperatureor less during the starting of operation of the fuel cell.